Fluid actuator with lock and cushion

ABSTRACT

A fluid actuator in the form of a differential fluid pressure operated piston rod in a cylinder has the piston rod retained in a retracted position by a spring biased pin and lock arrangement which in its normal biased position has the lock in locking engagement with the piston rod, the lock and pin being acted upon by the fluid pressure to effect its unlocking from the piston rod, a cushion cup being positioned behind the enclosed end of the piston rod to move axially upon movement of the piston rod into position to restrict movement of the lock into its normal locking position.

United States Patent Wagner I [54] FLUID ACTUATOR WITH LOCK AND' CUSHION[72] Inventor: Douglas A. Wagner, Indianapolis,

Ind.

[73] Assignee: General Motors Corporation,

Detroit, Mich.

[22] Filed: Oct. 27, 1971 211 App]. No.: 193,055

52 US. Cl ..92/24, 74/527 [51] Int. Cl ..F15b 15/26 [58] Field of Search....92/l5, 24, 27, 28, 30', 188/67; 1 74/527; 251/94 [56] ReferencesCited UNITED STATES PATENTS 2,130,618 9/1938 Gnavi ..92 27- 2,815,73612/1957 Wright ..92/24 3,398,651

8/1968 Folmer ..92/27 Oct. 24, 1972 3,584,544 6/1971 Haberman ..92/24FOREIGN PATENTS OR APPLICATIONS 943,791 3/1949 France ..74/527 PrimaryExaminer-Martin P. Schwadron Assistant Examiner-A. HershkovitzAttorney-J. L. Carpenter et a1.

[57] ABSTRACT A fluid actuator .in the form of a differential fluidpres-- sure operatedpiston rod in a cylinder has the piston rod retainedin a retracted position by a spring biased pin and lock arrangementwhich in its normal biased position has the lock in looking engagementwith the piston rod, the lock and pin being acted upon by the fluidpressure to effect its unlocking from the "piston rod, a cushion cupbeing positioned behind the enclosed end of the piston rod to moveaxially upon movement of the piston rod into position to restrictmovement of the lock into its normal locking position.

7 Claims, 2 Drawing Figures FLUID ACTUATOR WITH LOCK AND CUSHION Thisinvention herein described was made in the course of work under acontract or subcontract thereunder with the Department of Defense.

This invention relates to a fluid actuator which is adapted to beoperated and controlled by pneumatic or hydraulic fluid under pressureand, in particular, to a differential fluid pressure operated actuatorhaving a locking mechanism and a cushion mechanism for the piston rod ofthe unit.

The device of this invention falls generally into a class of actuatorswhich are described as linear actuators. By the word linear, it is meantthat the actuating device operates in a straight line.

Linear actuators of the piston type are usually con trolled by hydraulicor pneumatic amplifiers such as, for example, a pneumatic or hydraulicservo valve.

Although the device of this invention may be utilized either as apneumatic or hydraulic device, it is described herein as a hydraulicfluid actuator.

It is sometimes desirable to use hydraulic fluid actuators in systemswherein the actuator is operated upon by hydraulic fluid at relativelyhigh pressure such that although a pressure differential normally existsonopposite sides of the piston of the actuator, the pressure on the lowpressure side of the piston may still be in the range of up to 400pounds per square inch pressure. Under these circumstances, if there isa malfunction in the unit, this relatively high pressure fluid on thelow pressure side of the piston is still sufficient to actuate thepiston if there is a sudden pressure drop opposing this fluid.Accordingly, it is desirable to provide a positive locking mechanism forthe piston in such a fluid actuator. in addition, it is also desirablein many circumstances, due to the shortness of the stroke of the pistonand the fluid pressures used in the unit, to provide a reasonablecushioning effect on the piston as it is moved on its return stroke.

lt is, therefore, a primary object of this invention to improve anactuator whereby a positive locking mechanism is provided to retain thepiston rod of the actuator in its retarded position while stillpermitting unlocking of this locking mechanism when desired to effectlinear movement of the piston rod.

Another object of this invention is to improve a fluid actuator toprovide it with a locking mechanism to engage and lock the piston rod inits retracted position when desired and to unlock this locking mechanismfrom the piston rod to permit a forward stroke, with a cushioningmechanism being provided to retain the locking mechanism in an unlockedposition until return of the piston rod to its retracted position, thecushioning mechanism also effecting a controlled return of the piston toits retracted position.

These and other objects of the present invention are attained by meansof a fluid actuator having a piston rod reciprocably mounted therein formovement from a retracted position to an extended position, a radiallyextending spring biased pin forcing a lock mechanism into lockingengagement with the piston rod when in its retracted position, the lockcarrying radially positioned detent balls engagable with the walls of asleeve in which the lock mechanism is slidably positioned to hold thelock in its radiallyextended locking position until fluid pressure actsupon the pin to permit radially inward movement of the ball detents toeffect release of the lock which is then actuated by fluid pressure outof locking engagement with the piston rod. A spring biased cushion cuppositioned axially behind the piston rod is movable by the springuponmovement of the piston rod into position in abuttingrelationship'against the lock to permit its engagement with the pistonrod on the piston rod when returned to its retracted position.

For a better understanding of the invention, as well as other objectsand further features thereof, reference is had to the following detaileddescription of the invention to be read in connection with theaccompanying drawings, wherein:

FIG. 1 is a plan view in section of the fluid-actuator with lock andcushion of the invention, with the lock engaging the piston rod of theactuator; and,

FIG. 2 is a view similar to FIG. 1 but with the lock disengaged from thepiston rod and contacting the cushion of this mechanism.

Referring now to the drawings, there is shown a fluid actuator mechanismincluding a plunger or piston rod 10 slidably positioned in an actuatorhousing 12, one end or free end 10a of the piston rod extendingexternally of the housing for connection to a suitable element, notshown, to be acted on by the actuator. In the embodiment disclosed, theactuator housing 12 consists of a cylinder 14 provided with reduced endportions 14a at opposite ends thereof received in the stepped bores 16and 18, of front and rear cylinder heads 20 and 22, respectively,'thelatter being secured together by equally spaced bolts 24 extendingthrough front head 20 and threaded into rear head 22 with the cylinder14 securely sandwiched between these heads.

Piston rod 10 is provided at one end with spaced apart rigid pistonflanges 26 and 28 slidably received in the bore 30 of cylinder 14, apiston seal in the form of annular retainers 32 and packing ring seal 34being positioned between these flanges. Adjacent to piston flange 26,the piston rod is formed with an annular groove provided by a reducedlock engaging portion 36 adjacent to the tapered spool end 38 of reduceddiameter of the piston rod.

The bore 18 in rear head 22 is closed byv a rear cover 40 having anaxial extending annular flange 42 extending into an enlarged portion ofthe bore 18, the flange 42 slidably carrying a cushion cup 44 having anaxially aligned aperture 45 through its radial wall, for a purpose to bedescribed. The cushion cup 44 is normally biased to the right, as seenin these figures, towards the piston rod 10 by means of a spring 46which abuts at one end against the inner wall of cover 40 and, at itsother end, abuts against the radial wall of cup 44, with movement of thecup in this direction being limited by a radial wall 48 of rear head 22.In this spring biased position of the cup 44, it will be adjacent thelock 60, to be described in detail hereinafter, to limit or inhibit itsmovement into the path of the piston rod 10.

Fluid ports 50 and 52 are positioned to introduce fluid into cylinder 14on opposing sides of piston flanges 26 and 28, the ends of the cylinder14 being notched at 14b to permit fluid entry into the bore 30 of thecylinder. Fluid ports 50 and 52 are in communication, for example, witha source of hydraulic fluid at different pressures through a servovalve, not shown, by means of upset headed tubes 51 and 53,respectively,

held in place on the front and rear cylinder heads and 22 by plates 54and 56, respectively.

To releasably-lock the piston rod in its retracted position, there isprovided the lock 60, in the form of a permit lock 60 to move into thebore 18 in the rear head 22 into and out of engagement with the annulargroove in the piston rod adjacent its spool end. The sleeve 64 is heldaxially in position by means of 1 a flanged cup-shaped cover 66 securedto the rear head 22 with the closed bore 67 of this cover concentricwith the stepped bore 65 through sleeve 64. As shown, lock 60 isprovided with an enlarged portion 60a at one end and a reduced portion60b at its opposite end terminating in a frusto-conical end portion 600,and a lock tip 60d. Passages 60s through the frusto-conical end portion600 communicatewith the axial stepped bore 61 in the lock. In addition,a plurality of circular apertures 60f extend radially outward throughthe wall of the lock, four in the embodiment disclosed, approximatelymidway of the reduced portion 6017, these apertures 60f being of adiameter to slidably receive the detent balls The detent balls 70 areadapted to move radially outward with respect to the outer periphery ofthe lock 60 for engagement against the chamfered shoulder 64a of anannular detent receiving groove provided at one end of the sleeve 64, sothat when the balls are thus positioned, as shown in FIG..1, the lock isprevented from moving axially to an unlocked position with respect tothe piston rod 10, that is to say, the lock 60 is maintained in a lockedposition with respect to the piston rod as shown in this figure;

Radial movement of the balls 70, and therefore of the lock 60, iscontrolled by a release pin 72 slidably received within the bore 61 inthe lock 60 with this pin being normally biased into engagement with thelock by means of a spring 74 partly housed within the cover 66 andencircling one end or lower end of the pin, as seen in the figures, withthe spring abutting at one end against the closed end of cover 66 and atits other end against an annular flange 72a on the pin 72. At itsopposite end, the pin 72 is provided with a reduced portion 72b with atapered shoulder 72c extending between this reduced portion of the pinand the nominal diameter portion of the pin. The reduced portion 72b ofthe pin 72 is of such a diameter that when this portion of the pin isadjacent to the balls 70, there is provided an annular cavity betweenthis portion of pin 72 and the inner wall of lock 60 so the balls canmove radially inward to release the lock 60 with respect to the sleeve64 so that the lock may be moved inward or downward as seen with respectto FIG. 1, out of locking engagement with the piston rod.

The spring 74 and the working diameter of the release pin 72 againstwhich hydraulic pressure acts, since the release pin is in effect asecondary piston within the lock which is also a piston, are so selectedthat the lock 60 will be forced by the pin 72, the shoulder 72a of whichengages one end of the lock, into actuator is below 400 pounds persquare inch.

In operation of the actuator in the particular application referred toabove, when the piston rod 10 is in its normal retracted position asshown in FIG. I, the

hydraulic fluid pressure in port 52 would be 400 pounds per square inchor less and, the cup 44 and the lock components, including lock 60, pin72, balls 70, would be in the positions as shown in this figure. Thelock 60 prevents movement of the piston rod 10 forward to its extendedposition, to the right as seen in these figures, by bearing against thelocking surface 36 or against the tapered edge of the spool end 38 ofthe piston rod. Although one end of the spool end 38 of the piston rodis tapered, it cannot function as a detent release mechanism withrespect to the lock 60 because the balls now extending radially outwardof the peripheral surface of the lock prevent the lock 60 from movingaxially inward, downward with respect to the view in FIG. 1, in thesleeve 64 out of engagement with the piston rod 10.

When hydraulic fluid at a pressure above 400 pounds per square inch issupplied to port 52, it will effect release of the lock 60 in thefollowing manner. The spring 74 holds the release pin 72 in the positionshown in-FlG. 1 until the pressure of hydraulic fluid entering throughthe passages 60e in the lock exceeds 400 pounds per square inch.Hydraulic fluid pressure over 400 pounds per square inch forces therelease pin 72 to move inward against the biasing action of spring 74.Movement inward of the release pin 72 brings its reduced end portion 72bto a position adjacent to the apertures 60f in the lock 60 to provide anannular chamber between this reduced portion 7 2b and the interior ofthe lock 60 so that the balls 70 can move radially inward out ofengagement with the chamfered shoulder 64a of the sleeve 64. Thismovement of the balls 70 is forced because the balls are seated on thechamfered shoulder surface 64a of the sleeve 64 and the hydraulic fluidpressure entering port 52 acting on the exposed-end portion of the lock60 is forcing the lock inward in the direction the release pin 72 hasjust moved.

When the balls 70 have moved into the space created by movement of therelease pin 72 as just described, the lock 60, pin 72 and balls 70 canmove inward, down as seen in FIG. 1, against the biasing action ofspring 74. As the lock 60 is moved inward to release the piston rod, thelatter is free to move as a result of hydraulic fluid pressure enteringthrough port 52 acting against the piston flange 26 of the piston rod tomove it to its extended position, to the right as seen in the figures.It is, of course, realized that as high pressure fluid is permitted toflow to port 52, port 50 is vented to the low pressure side of thehydraulic system.

As the piston rod moves to the extended position, the cup 44 is biasedin the same direction under theinfluence of spring 46 until its axialmovement is stopped by the shoulder 48 in the bore 18 of the rear head22. With the cup 44 in this position, as shown in FIG. 2, the lock 60,which has previously been'moved inward in the manner just described, isnow prevented from returning to its original position, should thehydraulic pressure at port 52 drop below 400 pounds per square inch.When it is desired to retract the piston rod 10, pressure is released atport 52 and applied through port 50 to act onthe piston flange 28 of thepiston rod tomove it towards the retracted position, to the left fromits position as seen in FIG. 2. As the piston rod retracts, the spoolend 38 of the piston rod engages the cup 44 closing the aperture 45therein so that further retraction of the piston rod forces oil to flowout from the back of the cup between the cup 44 and the annular flange42 of the cover 40. This flow of hydraulic fluid is restricted becauseof the close fit between the peripheral wall of the cup 44 and theannular interior wall of the flange 42, thus providing a hydrauliccushion at the end of the retracted stroke of the piston rod.

When the cup 44 is moved axially, to the left from the position shown inFIG. 2, it will uncover the lock 60 to permit the latter to move outwardfrom the position shown in FIG. 2 to that shown in FIG. 1 to lock thepiston rod in the retracted position until the hydraulic pressure atport 52 is again raised above 400 pounds per square inch.

Thus, as the hydraulic pressure at port 52 is reduced to 400 pounds persquare inch or less, the spring 74 will be able to force release pin 72outward, upward in terms of the figures, but its movement and that oflock 60 is at first prevented by engagement of the lock 60 against cup44. However, as cup 44 is moved out of the way by return movement of thepiston rod toward its retracted position, the release pin 72 by thebiasing action of spring 74 moves outward so that its tapered portion72c engages the balls 70, held in axial position with respect to thelock in the apertures 60f, to move them and the lock 60 axially upwardwith respect to the sleeve 64 until such time as the apertures 60f inthe lock are opposite the annular groove and the shoulder 64a of thesleeve at which time the balls 70 are cammed radially outward by theinclined surface of the tapered portion 72c of the pin 72. The releasepin then moves upward relative to the lock until its nominal diameterportion is adjacent to the balls to prevent their return movementradially inward. As this occurs, the pin 72, having moved relative tothe lock 60, now has its flange 7 2a abutting against the bottom of thelock so that the spring 74 now biases the lock and pin to the lockposition relative to the piston rod as seen in FIG. 1.

What is claimed is:

1. A linear actuator comprising, in combination, an actuator housingincluding piston cylinder means closed at one end, piston meanspositioned to move in said piston cylinder means between a retractedposition and an extended position with one end of said piston meansextending externally of said actuator housing, a lock groove in saidpiston means at its other end, said actuator housing including means forapplying fluid pressure to said piston means to selectively move saidpiston means between said retracted position and said extended position,a lock receiving bore in said housing in communication with said pistoncylinder means, a lock piston means p sitioned to move in said lockreceiving bore from a first position engaging said groove to a secondposition out of engagement therewith, spring means positioned tonormally bias said lock piston means to said first position, said lockpiston means including releasable detent means operable to releasablyretain said lock piston means in said first position and pressureactuated means operable to release said detent means.

2. A linear actuator according to claim 1 wherein said lock receivingbore includes an enlarged bore portion adapted to receive said detentmeans and wherein said lock piston means includes a lock in the form ofa piston partly open at one end and open at its other end with radialapertures through the side walls thereof, said detent means includingdetent balls slidably received in said apertures, a release pin slidablyreceived in said lock to control the radial position of said detentballs in said apertures, and spring means adapted to bias said releasepin in a direction to force said detent balls into locking engagementwith said enlarged bore portion and to normally bias said lock to saidfirst position.

3. A linear actuator according to claim 1, further including anapertured cushion cup slidably positioned in the closed end of saidpiston cylinder means and second spring means positioned to normallybias said cushion cup to a position adjacent said lock receiving borewhen said piston means is moved toward said extended position toreleasably block movement of said lock piston means as it moves fromsaid second position toward said first position, said cushion cup beingmovable against said second spring means by said piston means uponmovement of said piston means to said retracted position.

4. A linear actuator including an actuator housing having an axial boretherein closed at one end and including a bored piston cylinder, apiston means positionedto move in said actuator housing and in saidpiston cylinder from a retracted position to an extended position withone end of said piston means extending externally from said actuatorhousing, said piston means having an annular groove at its opposite end,bore means in said actuator housing normal to said axial bore andpositioned in alignment with said groove of said piston means when saidpiston means is in said retracted position, a lock, in the form of ahollow piston with a groove engaging portion at one end, slidablypositioned in said bore means for movement from a first position inwhich said lock engages in said annular groove of said piston means to asecond position in which said lock is out of engagement with said pistonmeans, said bore means including an annular ball receiving detent means,said lock having apertures through the walls thereof, detent ballsslidably received in the apertures in said lock for movement radiallyoutward into said ball receiving detent means to lock said lock in saidfirst position, said detent balls being also movable radially inward torelease said lock for axial movement in said bore means to said secondposition, and a spring biased release pin slidably received in the openend of said lock, said release pin having a cam portion thereon toeffect radial outward movement of said detent balls and a reduceddiameter portion to pro vide a cavity between said reduced portion andthe interior of said lock to permit radial inward movement of saiddetent balls, and means for applying fluid pressure to said piston meansand to said lock and release pin.

5. A linear actuator according to claim 4 further including an aperturedcushion cup slidably positioned in the closed end of said axial bore andspring means in said axial bore to normally bias said cushion cup to aposition in said axial bore to partly cover said bore means when saidpiston means is moved toward said extended position and said lock ismoved to said second position and movable to uncover saidv bore meansupon movement of said piston means to said retracted position.

6. A linear'actuator comprising an actuator housing means, a first'borein said housing closed at one end, and a second bore in said housing atright angles to said first bore and in communication at one endtherewith, a

first piston means positioned to slide in said first bore,

means in said actuator housing means for introducing fluid pressure toopposing sides of said first piston means to effect selected movement ofsaid first piston means from a retracted position to an extendedposition, an annular groove in said first piston means axiallypositioned thereon to be adjacent said second bore when said firstpiston means is in said retracted posiion, a second piston meansslidably positioned in said second bore to move into and out ofengagement with said annular groove of said first piston means, saidsecond piston means including an outer piston lock means with radiallymovable detentmeans thereon engagable in said second bore when saidouter piston lock is in engagement with said annular groove, an innerpiston release pin positioned to slide in said second bore and in saidouter piston lock to controlmovement of said detent means and, springmeans adapted to bias said piston release pin into said outer pistonlock and to bias said outer piston lock into engagement with saidannular groove, said detent means being positionable to lock said outerpiston lock into engagement with said annular groove.

7. A linear actuator according to claim 6 further .including anapertured cushion cup slidably positioned in said first bore between theclosed end thereof and said first piston means, and second spring meansin said first bore adapted to bias said apertured cushion cup to aposition to partly cover said second bore to restrict movement ofsaid-outer piston lock against the biasing action of said spring meanswhen said first piston means is moving to and from said extendedposition, said apertured cushion cup being moved against the biasingaction of said second spring means by said first piston means as it ismoved from said extended position to said retracted position.

1. A linear actuator comprising, in combination, an actuator housingincluding piston cylinder means closed at one end, piston meanspositioned to move in said piston cylinder means between a retractedposition and an extended position with one end of said piston meansextending externally of said actuator housing, a lock groove in saidpiston means at its other end, said actuator housing including means forapplying fluid pressure to said piston means to selectively move saidpiston means between said retracted position and said extended position,a lock receiving bore in said housing in communication with said pistoncylinder means, a lock piston means positioned to move in said lockreceiving bore from a first position engaging said groove to a secondposition out of engagement therewith, spring means positioned tonormally bias said lock piston means to said first position, said lockpiston means including releasable detent means operable to releasablyretain said lock piston means in said first position and pressureactuated means operable to release said detent means.
 2. A linearactuator according to claim 1 wherein said lock receiving bore includesan enlarged bore portion adapted to receive said detent means andwherein said lock piston means includes a lock in the form of a pistonpartly open at one end and open at its other end with radial aperturesthrough the side walls thereof, said detent means including detent ballsslidably received in said apertures, a release pin slidably received insaid lock to control the radial position of said detent balls in saidapertures, and spring means adapted to bias said release pin in adirection to force said detent balls into locking engagement with saidenlarged bore portion and to normally bias said lock to said firstposition.
 3. A linear actuator according to claim 1, further includingan apertured cushion cup slidably positioned in the closed end of saidpiston cylinder means and second spring means positioned to normallybias said cushion cup to a position adjacent said lock receiving borewhen said piston means is moved toward said extEnded position toreleasably block movement of said lock piston means as it moves fromsaid second position toward said first position, said cushion cup beingmovable against said second spring means by said piston means uponmovement of said piston means to said retracted position.
 4. A linearactuator including an actuator housing having an axial bore thereinclosed at one end and including a bored piston cylinder, a piston meanspositioned to move in said actuator housing and in said piston cylinderfrom a retracted position to an extended position with one end of saidpiston means extending externally from said actuator housing, saidpiston means having an annular groove at its opposite end, bore means insaid actuator housing normal to said axial bore and positioned inalignment with said groove of said piston means when said piston meansis in said retracted position, a lock, in the form of a hollow pistonwith a groove engaging portion at one end, slidably positioned in saidbore means for movement from a first position in which said lock engagesin said annular groove of said piston means to a second position inwhich said lock is out of engagement with said piston means, said boremeans including an annular ball receiving detent means, said lock havingapertures through the walls thereof, detent balls slidably received inthe apertures in said lock for movement radially outward into said ballreceiving detent means to lock said lock in said first position, saiddetent balls being also movable radially inward to release said lock foraxial movement in said bore means to said second position, and a springbiased release pin slidably received in the open end of said lock, saidrelease pin having a cam portion thereon to effect radial outwardmovement of said detent balls and a reduced diameter portion to providea cavity between said reduced portion and the interior of said lock topermit radial inward movement of said detent balls, and means forapplying fluid pressure to said piston means and to said lock andrelease pin.
 5. A linear actuator according to claim 4 further includingan apertured cushion cup slidably positioned in the closed end of saidaxial bore and spring means in said axial bore to normally bias saidcushion cup to a position in said axial bore to partly cover said boremeans when said piston means is moved toward said extended position andsaid lock is moved to said second position and movable to uncover saidbore means upon movement of said piston means to said retractedposition.
 6. A linear actuator comprising an actuator housing means, afirst bore in said housing closed at one end, and a second bore in saidhousing at right angles to said first bore and in communication at oneend therewith, a first piston means positioned to slide in said firstbore, means in said actuator housing means for introducing fluidpressure to opposing sides of said first piston means to effect selectedmovement of said first piston means from a retracted position to anextended position, an annular groove in said first piston means axiallypositioned thereon to be adjacent said second bore when said firstpiston means is in said retracted position, a second piston meansslidably positioned in said second bore to move into and out ofengagement with said annular groove of said first piston means, saidsecond piston means including an outer piston lock means with radiallymovable detent means thereon engagable in said second bore when saidouter piston lock is in engagement with said annular groove, an innerpiston release pin positioned to slide in said second bore and in saidouter piston lock to control movement of said detent means and, springmeans adapted to bias said piston release pin into said outer pistonlock and to bias said outer piston lock into engagement with saidannular groove, said detent means being positionable to lock said outerpiston lock into engagement with said annular groove.
 7. A linearactuator according to claim 6 further including an apertured cushion cupslidably positioned in said first bore between the closed end thereofand said first piston means, and second spring means in said first boreadapted to bias said apertured cushion cup to a position to partly coversaid second bore to restrict movement of said outer piston lock againstthe biasing action of said spring means when said first piston means ismoving to and from said extended position, said apertured cushion cupbeing moved against the biasing action of said second spring means bysaid first piston means as it is moved from said extended position tosaid retracted position.